AMD Am186 Series, Instruction Set

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Instruction Set 4-57
HLT Halt HLT
What It Does
HLT causes the microcontroller to suspend instruction execution until it receives an interrupt
request or it is reset.
Syntax
Description
HLT places the microcontroller in a suspended state, leaving the CS and IP registers
pointing to the instruction following HLT. The microcontroller remains in the suspended
state until one of the following events occurs:
n
An external device resets the microcontroller by asserting the RES signal.
The microcontroller immediately clears its internal logic and enters a dormant state.
Several clock periods after the external device de-asserts RES, the microcontroller
begins fetching instructions.
n
The Interrupt-Enable Flag (IF) is 1 and an external device or peripheral asserts one of
the microcontroller’s maskable interrupt requests that is not masked off by its interrupt
control register (or an external device issues a nonmaskable interrupt request by
asserting the microcontroller’s nonmaskable interrupt signal).
The microcontroller resumes executing instructions at the location specified by the
corresponding pointer in the microcontroller’s interrupt vector table. After the interrupt
procedure is done, the microcontroller begins executing the sequence of instructions
following HLT.
Operation It Performs
Flag Settings After Instruction
Form Opcode Description
Clocks
Am186 Am188
HLT F4 Suspend instruction execution 2 2
HLT
stopExecuting();
/* CS:IP points to the following instruction */
/* wait for interrupt or reset */
do {
} while (!(interruptRequest() || nmiRequest() || resetRequest()))
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Processor Status
Flags Register
reserved
OF DF IF TF SF ZF AF PF CF
? = undefined; – = unchanged
– – – – – – res – res – res –